JPH054629Y2 - - Google Patents

Description

[Detailed explanation of the invention] A. Purpose of the invention (1) Industrial application field This invention is a hydraulic system for a work vehicle, particularly a hydraulic pump; a hydraulic cylinder that is released to lower the working machine; a check valve that is interposed in a control oil passage between a discharge port of the hydraulic pump and the hydraulic cylinder to prevent the release of hydraulic pressure from the hydraulic cylinder; a manual valve interposed in the control oil passage between the valve and the discharge port; and a valve-opening rod that forcibly opens the check valve in conjunction with the manual valve; a neutral position communicating the valve with the oil tank;
a rise control position shifted in one direction from the neutral position to communicate the check valve with the discharge port;
The present invention relates to an improvement in a device configured to be shifted from the neutral position to the other position to communicate the check valve with the oil tank and to take a lower control position in which the check valve is opened by the valve opening rod.

(2) Conventional technology Conventionally, the manual valve is configured to be operated only by input.
(See Publication No. 125818).

(3) Problems to be solved by the invention In the above hydraulic system, when the manual valve is shifted from the neutral position to the lowering control position in order to lower the work equipment, the hydraulic pressure acting on the check valve in the valve closing direction is resisted. Since the check valve must be forcibly opened using the valve opening rod, if the manual valve is configured to be operated only by input as in the past, a relatively large operating force is required, making it difficult to operate the manual valve. becomes heavy.

In view of the above, an object of the present invention is to provide the above-mentioned hydraulic system that allows the manual valve to be easily operated from the neutral position to the descending control position.

B. Structure of the invention (1) Means for solving the problem The present invention is characterized in that the manual valve is provided with an urging means for urging it from the neutral position to the descending control position.

(2) Effect With the above configuration, when the manual valve is shifted from the neutral position to the downward control position, a biasing force is applied to the manual valve in the shifting direction, so that the manual valve can be operated easily. be exposed.

(3) Embodiment An embodiment of the present invention will be explained with reference to the drawings. First, in FIG. 1, reference numeral 1 indicates an agricultural tractor, in which an engine 3 is mounted on the front part of a body frame 2, and a pair of left and right front wheels. 5, 5 are suspended so that they can be steered. A transmission unit 4 is attached to the rear end of the vehicle body frame 2, and a pair of left and right rear wheels 6, 6 are suspended below the transmission unit 4 so as to be steerable. Further, a seat 7 for a worker is installed on the transmission unit 4.

A handle column 8 is erected on the vehicle body frame 2 at an intermediate position between the seat 7 and the engine 3, and a handle wheel 9 for steering the front and rear wheels 5, 5, 6, 6 is pivotally supported on this. Ru.

The transmission unit 4 is constructed by integrally coupling a clutch 10, a transmission 11, and a rear differential 12, and a crankshaft 14 of the engine 3 is connected to an input shaft 13 of the clutch 10 via a drive shaft 15. Ru. The rear differential device 12 is arranged between the left and right rear wheels 6, 6 so as to be able to drive them. Further, a front differential device 16 is disposed between the left and right front wheels 5, 5 to drive these, and its input member is the propulsion shaft 1.
It is connected to the output member of the transmission 11 via 7.

Therefore, while the engine 3 is operating, its power is transmitted to the rear wheels 6, 6 via the drive shaft 15, clutch 10, transmission 11, and rear differential 12, and is further transmitted from the transmission 11 to the propulsion shaft 17. The power is then transmitted to the front wheels 5, 5, allowing all wheels to be driven simultaneously.

At the front end of the vehicle body frame 2, a front lifting arm 21f having a hitbox 20f for connecting a working machine at the front end is pivotally supported so as to be swingable up and down. A piston 23f of a front hydraulic cylinder 22f installed on the vehicle body frame 2 is connected to this front lifting arm 21f via a link mechanism 24f.
The front lifting arm 21f is raised by the hydraulic drive of the pump 3f, and the lifting arm 21f is lowered by its own weight by releasing the hydraulic pressure.

Further, at the rear end of the transmission unit 4, a rear lifting arm 21r having a hitbox 20r for connecting a working machine at the rear end is pivotally supported so as to be able to swing up and down. A piston 23r of a rear hydraulic cylinder 22r installed on the transmission unit 4 is connected to the rear lifting arm 21r via a link mechanism 24r, and the rear lifting arm 21r is hydraulically driven by the piston 23r.
is raised, and the elevating arm 21r is lowered by its own weight by releasing hydraulic pressure.

A hydraulic control unit 25 is attached to the transmission unit 4 for controlling the operation of the front and rear hydraulic cylinders 22f and 22r. This hydraulic control unit 2
5 is connected to an oil tank 26 installed adjacent thereto via a suction pipe 27 and a return pipe 28 (see FIG. 9), and is connected to front and rear hydraulic cylinders 22f, 22r via hydraulic conduits 29f, 29r. It also communicates with the hydraulic chamber 26, so that the hydraulic oil sucked from the oil tank 26 can be force-fed to each hydraulic cylinder 22f, 22r, and the hydraulic oil can be returned to the oil tank 26.

The hydraulic control unit 25 also includes first and second control levers 3 disposed beside the seat 7.
1 and 32, operation of the front and rear hydraulic cylinders 22f and 22r is selected by operating the first control lever 31, and hydraulic pressure is applied to the selected hydraulic cylinder 22f or 22r by operating the second control lever 32. Transmission and release can be controlled.

Hereinafter, the second part regarding this hydraulic control unit 25 will be explained.
This will be explained in detail with reference to FIGS.

As shown in FIGS. 2 and 4, the hydraulic control unit 25 is composed of a hydraulic pump 33 and a control valve device 34 that are arranged adjacent to each other in the left and right direction of the tractor 1, and both 33 and 34 are connected to the unit. A casing 35 is commonly used for this purpose.
This casing 35 is connected to a plurality of bosses 36a, 3 protruding from the front surface of the casing 36 of the transmission unit 4.
The hydraulic control unit 25 is attached to the transmission unit 4 by fixing it to the transmission unit 6a with a plurality of bolts 37, 37.

As shown in FIG. 6, the hydraulic pump 33 is configured in a gear type having a pair of pump gears 39 and 40 that are housed in a gear chamber 38 of a casing 35 and mesh with each other.
One end of a, 40a is connected to the front end plate 41 that closes the front surface of the gear chamber 38, and the other end is connected to the pump gear 39,
40 and are respectively supported by bearing blocks 42 fitted in the gear chamber 38, and this bearing block 42
is positioned by being fitted with a rear end plate 43 that closes the rear surface of the gear chamber 38. And both end plates 41, 43
are connected to each other with the casing 35 in between by a plurality of through bolts 44, 44.

One pump gear 3 is mounted on the back of the rear end plate 43.
A connecting cylinder 43a that faces the shaft 39a of 9 inward is integrally protruded, and this connecting cylinder 43a connects to the power outlet 45 that opens into the casing 36 of the transmission unit 4 when the casing 35 is attached to the transmission unit 4. A shaft 39a of the pump gear 39 is connected via a joint 48 to a pump drive shaft 47 that is fitted into the pump via a seal member 46 and interlocks with the input member of the clutch 10. Since the hydraulic pump 33 is driven by the input member of the clutch 10 in the transmission unit 4 in this way, the hydraulic pump 33 is always maintained in an operating state while the engine 3 is operating, regardless of whether the clutch 10 is open or closed, and the hydraulic can be ensured.

The casing 35 includes both pump gears 39 and 40.
A suction port 50 and a discharge port 51 are provided which open into the gear chamber 38 across the meshing portion of the gear chamber 38 . These ports 50 and 51 are arranged linearly along the arrangement direction of the hydraulic pump 33 and the control valve device 34. In this arrangement, after casting the casing 35, the shell cores of each part are connected to the ports 50, 51.
It is effective in easily discharging through the water.

A connecting short pipe 52 is fitted into the input of the suction port 50, and the suction pipe 27 is connected to this.

The control valve device 34 is shown in FIGS. 7, 9 and 1.
As shown in Figure 2, the front and rear hydraulic cylinders 22
A switching valve 55 that selects the operation of the hydraulic cylinders 22f and 22r, a manual valve 56 that controls the transmission and release of hydraulic pressure to the selected hydraulic cylinder 22f or 22r, a throttle valve 57 that adjusts the operating speed of each hydraulic cylinder 22f and 22r, A check valve 58 that prevents the release of hydraulic pressure from each hydraulic cylinder 22f, 22r and stops its return movement, a first relief valve 59 that defines the upper limit of the discharge pressure of the hydraulic pump 33, and a second relief valve that prevents overload. It consists of a relief valve 60, which is housed in the casing 35 as follows.

That is, as shown in FIGS. 3, 7, and 8, the casing 35 has a first valve hole 61 that extends perpendicularly to the arrangement direction of the hydraulic pump 33 and the control valve device 34, and a a second valve hole 62 extending above and parallel to the second valve hole 61; a third valve hole 63 extending above the second valve hole 62 in the arrangement direction of the hydraulic pump 33 and the control valve device 34;
A fourth valve hole 64 is bored above and parallel to the fourth valve hole 64, and a manual valve 56 is installed in the first valve hole 61.
The second valve hole 62 has a check valve 58 and a second relief valve 60, and the third valve hole 63 has a throttle valve 57.
A switching valve 55 is disposed in each of the fourth valve holes 64, and a first relief valve 59 is built in the manual valve 56.

In FIG. 9, the outlet of the discharge port 51 of the hydraulic pump 33 opens directly into the first valve hole 61, thereby allowing the hydraulic pump 33 and the control valve device 34 to communicate with each other.

Further, a supply port 65 and a discharge port 66 are opened in the first valve hole 61 with the outlet of the discharge port 51 interposed therebetween, and the outlet of the supply port 65 is opened in the second valve hole 62 . A high pressure port 67 opens in the second valve hole 62, a central port 68 opens in the fourth valve hole 64, and an oil passage 69 connects these ports 67 and 68.
A throttle hole 70 coaxial with the third valve hole 63 is formed in the middle of the valve hole 63 . Furthermore, the fourth valve hole 64 has a central port 6.
A pair of front and rear output ports 71f, 7 across 8
1r is open, and these output ports 71f, 71r
front and rear hydraulic cylinders 22f, 22r at the outlet of
The hydraulic conduits 29f and 29r are connected to the hydraulic conduits 29f and 29r, respectively.

Therefore, the front (rear) hydraulic cylinders 22f, 2
Control oil passage L that communicates between 2r and the discharge port 51
are the first valve hole 61, the supply port 65, and the second valve hole 6.
5, high pressure port 67, oil path 69, center port 6
8. Consists of a switching valve 55, output ports 71f, 71r, and hydraulic conduits 29f, 29r.

The outlet of the discharge port 66 is connected to the casing 35.
The return pipe 2 communicates with the oil chambers 72 and 73 formed on both front and rear sides of the oil tank 26 via an oil passage 74, and connects to the oil tank 26 with an outlet 75 that opens into the front oil chamber 72.
8 is connected. Therefore, the oil discharged into the oil chambers 72 and 73 is returned to the oil tank 26.

The open surfaces of the oil chambers 72 and 73 are closed by rear end plates 76 and 77, respectively, before being fastened to the casing 35 with bolts 78 and 79 (fifth
(see figure).

Now, to explain the structure of each of the above-mentioned valves, first, the switching valve 55 has a fourth valve as shown in FIGS. 7 and 8.
The valve hole 64 is formed into a socket shape that rotatably fits into the valve hole 64, and by rotating the valve hole 64, the center port 68 can be selectively communicated with the front and rear output ports 71f and 71r. This switching valve 55 has one end protruding from the right side surface of the casing 35, and the first control lever 31 is attached to it. Therefore, by rotating the first control lever 31, the switching valve 55 is
is rotated.

A regulating plate 82 that regulates the rotation range of the first control lever 31 is fixed to the casing 35 with bolts 83 (see FIG. 5). This regulating plate 82 engages with a circumferential groove 84 (see FIG. 8) of the switching valve 55 and also functions to prevent it from coming off.

As shown in FIG. 9, the manual valve 56 is formed into a spool shape that slidably fits into the first valve hole 61, and has a neutral position A in the center, an upward control position B on one side, and a downward control position B on the other side. It is designed to take three positions including control position C. A pin 87 is provided on the side surface of one end of the manual valve 56 that protrudes into the rear oil chamber 73, and this pin 87 is attached to the second control lever 3.
A fork 88 fixed to the rotation shaft 32a of No. 2 is engaged. Therefore, by rotating the second control lever 32, the manual valve 56 is slidably operated.
In this case, the second control lever 32 is held at each position corresponding to the neutral, upward control, and downward control positions of the manual valve 50 by a holding member (not shown).

The manual valve 56 includes, in order from the left side in FIG. 9, a first land 90 ₁ and a first large groove 91 ₁ for discharge.
(See Figure 8), the first small groove 92 for the rising diaphragm.
₁ (see FIG. 10), a second land 90 ₂ , a second small groove 92 ₂ for descending throttle (see FIG. 11), and a second large groove 91 ₂ for discharge. At position A, the discharge port ₅₁ and the discharge port 66 are communicated through the first large groove 911, and the supply port 65, and therefore the check valve ₅₈ , are communicated with the oil tank 26 through the second small groove 922. , and in the ascending control position B, the first
The land 90 ₁ blocks the discharge port 51 and the discharge port 66, and the second land 90 ₂ blocks the supply port 65 and the front oil chamber 72, and at the same time, the discharge port ₅₁ and The supply port 65 and, therefore, the check valve 58 are communicated with each other, and at the lowering control position C, the second land ₉₀₂ blocks the discharge port 51 and the supply port 65, and the supply port is connected via the second large groove ₉₁₂ . 65, therefore, the check valve 58 and the front oil chamber 72 are communicated with each other. Further, at each intermediate position between the neutral position A, the ascending control position B, and the descending control position C, the first small groove 92 ₁ or the second small groove 92 ₂ intervenes in the hydraulic oil flow path.

Each of the above grooves 91 ₁ , 91 ₂ , 92 ₁ , 92 ₂
are formed by chamfering opposing portions of the outer peripheral surface of the manual valve 56. In this way, a sliding surface that is not cut into grooves remains on the outer periphery of the manual valve 56 over its entire length, so that good sliding performance of the valve 56 can be obtained.

The manual valve 56 has a large diameter valve chamber 93 extending in the axial direction, a small diameter guide hole 94 coaxially connected to the inner end of the valve chamber 93, and a guide hole 94 adjacent to the valve chamber 93. A through hole 95 that communicates with the one large groove 91 ₁ and a through hole 96 that opens the valve chamber 93 to the front oil chamber 72 are provided, and the inner end wall of the valve chamber 93 is formed in the valve seat 97 . The valve chamber 93 accommodates a conical valve 98 that cooperates with the valve seat 97 and a valve spring 99 that biases the valve 98 in the closing direction, that is, toward the valve seat 97. 59 are configured.

The conical valve 98 integrally includes a valve rod 98a that extends across the through hole 95, and a small piston 98b that is formed at the tip of the valve rod 98a and slides into the guide hole 94.

In the front oil chamber 72, a bolt 100 is screwed onto one end of the manual valve 56 so as to support a fixed end of a valve spring 99. At this time, a check valve (described later) is installed between the manual valve 56 and the bolt 100. The interlocking arm 101 for opening the valve 58 is clamped.

As clearly shown in FIG. 9A, the check valve 58 includes a valve cylinder 105 that is fitted into the second valve hole 62 and has one end communicating with the supply port 65;
It is comprised of a cup-shaped main valve 106 disposed within the main valve 106, a sub-valve 107 disposed within the main valve 106, and a valve spring 108 that biases the sub-valve 107 in the closing direction. The one end of the valve cylinder 105 is connected to the main valve 10
6, and at the end of the main valve 106 on the opposite side from the main valve seat 109, the main valve 106 is slidably engaged with the inner circumferential surface of the valve cylinder 105 to prevent the main valve 106 from tilting. A piston 106a is integrally provided.
A through hole 1 communicating the inside of the valve cylinder 105 with the high pressure port 67 before and after the piston 106a.
10 and 111 are bored in the valve cylinder 105.

The end wall of the cup-shaped main valve 106 is formed into a sub-valve seat 112 that cooperates with a sub-valve 107.
A piston 107a that slides on the inner peripheral surface of the main valve 106 at a position apart from the piston 107a is integrally connected to the sub valve 107, thereby preventing the sub valve 107 from tilting. A through hole 113 is formed in the main valve 106 between the piston 107a and the sub-valve seat 112, which communicates the inside of the main valve 106 with the outer circumferential side thereof.

The sub-valve 107 has a protruding shaft 1 passing through the sub-valve seat 112.
14 are integrally arranged in series, and this protruding shaft 114 has a two-step shape including a large diameter portion 114a on the proximal end side and a small diameter portion 114b on the distal end side. A valve opening rod 115 is disposed opposite the tip of the protruding shaft 114. The valve opening rod 115 is slidably supported on the partition wall between the second valve hole 62 and the front oil chamber 72, and is connected to the interlocking arm 101 in the front oil chamber 72, so that the manual valve 56 is in the neutral state. During the operation from position A to descending control position C, the protruding shaft 114 and the main valve 106 are sequentially pushed.

One end of the valve cylinder 105 is connected to the stepped portion 6 of the second valve hole 62.
2a, the second valve hole 62 is provided with a partition member 118 that abuts the other end of the valve cylinder 105.
At the same time, a hollow bolt 119 that fixes the partition member 118 is screwed. This bolt 1
The hollow portion 19 has its open end closed with a screw plug 120 to form a valve chamber 121, and on the side of this valve chamber 121, the partition member 118 has a valve seat 12 that communicates with the inside of the valve cylinder 105.
6 is formed. A ball valve 122 that cooperates with the valve seat 126, a retainer 123 that supports the ball valve 122 with a conical recess 123a on the front surface, and a valve that biases the ball valve 122 in the closing direction through the retainer 123. A spring 124 is housed in the valve chamber 121, and the second relief valve 60 is configured by these springs 124 and 124.

The valve chamber 121 is opened to the rear oil chamber 73 through a through hole 125 formed in the bolt 119.

Referring again to FIG. 9, the throttle valve 57 is connected to the third valve hole 6.
3 is screwed on. The throttle valve 57 has a tapered portion 57a inserted into the throttle hole 70 at its inner end, and a hexagonal head 57b at its outer end, which can be rotated by fitting a spanner into the head 57b. By this, the tapered portion 57a is rotated according to the rotation direction.
The opening degree of the throttle hole 70 can be increased or decreased by advancing and retreating, and the throttle hole 70 can be closed at its forward limit.

As clearly shown in Figures 3, 4, 7, and 9,
At the neutral position A of the manual valve 56, the oil passage 7
A hook-shaped portion 127a at one end of a coiled tension spring 127 as a biasing means loosely inserted into the interlocking arm 10
1, and the other end bent portion 127b is locked to the end surface of the oil passage 74 on the rear oil chamber 73 side. This tensile force of the tension spring 127 urges the manual valve 56 from the neutral position A to the downward control position C.

Arranging the tension spring 127 in the oil passage 74 as described above eliminates the need for the space occupied by the tension spring 127, which is effective in reducing the size of the casing 35. Furthermore, if the locking bent portion 127b is formed at the other end of the tension spring 127, the interlocking arm 101 is required to tension the tension spring 127.
A locking hole 12 for locking one end of a tension spring 127 to
8, therefore, the number of processing steps involved in tensioning the tension spring 127 is small, and furthermore, the tensioning work of the tension spring 127 is facilitated.

Further, as clearly shown in FIGS. 2 to 5, when the manual valve 56 is in the neutral position A, one end of the annular portion 129a of the coiled tension spring 129 is attached to the locking shaft 130 protruding from the end surface of the protrusion of the switching valve 55. The hook-shaped portion 129b at the other end is engaged with the second control lever 3.
It is locked in a locking hole 131 formed in the second U-shaped bracket 32b. In this case, the annular portion 129a
is formed to be elongated in the axial direction of the tension spring 129, and the locking shaft 130 is disposed coaxially with the switching valve 55.

With this configuration, when the second control lever 32 returns from the rotation position corresponding to the upward control position B of the manual valve 56 to the rotation position corresponding to the neutral position A of the manual valve 56, the second control lever 32 A tensile force of a tension spring 129 is applied.

Next, to explain the operation of this embodiment, FIG. 9 shows a state in which the manual valve 56 is placed at the neutral position A. If the hydraulic pump 33 is operating in this state, the hydraulic oil sucked from the oil tank 26 by the hydraulic pump 33 and discharged to the discharge port 51 is transferred to the first large groove 91 ₁ of the manual valve 56, the discharge port 66, Since the oil flows back to the oil tank 26 without resistance through the oil passage 74 and the front oil chamber 72, high oil pressure is not generated at the discharge port 51.

At this time, if the switching valve 55 is placed in a position communicating with the central port 68 and the rear output port 71r,
The hydraulic pressure generated in the hydraulic chamber of the rear hydraulic cylinder 22r due to the weight of the rear lifting arm 21r (actually, the weight of the work equipment connected to it is also added) is transferred to the switching valve 55,
The pressure is transmitted to the inside of the valve cylinder 105 of the check valve 58 through the throttle hole 70 and the high pressure port 67, and acts on the back surfaces of both the main and auxiliary valves 106, 107 to keep them closed, so that the rear hydraulic cylinder 22r
Hydraulic oil does not flow out, and the rear lifting arm 21r can maintain its current position.

The hitch box 20r of this rear lifting arm 21r
When the working machine connected to the machine receives an overload in the downward direction during work, the valve cylinder 1 of the check valve 58
05 rises, and the ball valve 122 of the second relief valve 60 receives the oil pressure at the front, and the valve spring 124
Since the valve opens while contracting, the excess oil pressure can be released to the rear oil chamber 73 side through the valve seat 126, the valve chamber 121, and the through hole 125, thereby protecting the working machine from overload.

Now, in order to raise the rear lifting arm 21r, the second
When the control lever 32 is rotated counterclockwise in FIG. 5 to shift the manual valve 56 to the ascending control position B, first, the first land ₉₀₁ blocks the discharge port 51 and the discharge port 66, and Since the supply port 65 and the front oil chamber 72 are cut off by the second land ₉₀₂ , the hydraulic pump 33
As a result, hydraulic pressure is generated at the discharge port 51. At the stage where the discharge port 51 is communicating with the supply port 65 via the first small groove ₉₂₁ ,
The above hydraulic pressure is transmitted to the supply port 65 side while being subjected to a throttling action in the first small groove 92 ₁ , and then acts on the front surface of the main valve 106 of the check valve 58 to push it open, thereby opening the main valve seat 109 and the valve cylinder 105 . Through hole 110,
High pressure port 67, throttle hole 70, center port 68,
The hydraulic pressure is transmitted to the hydraulic chamber of the rear hydraulic cylinder 22r through the switching valve 55 and the rear output port 71r, and this hydraulic pressure drives the piston 23r to move the rear lifting arm 2.
1r is increased, but the rate of increase is controlled to be slow mainly by the throttling action of the first small groove 92 ₁ of the manual valve 56 . The speed of this slow rise is determined by the speed of the throttle hole 70 caused by the throttle valve 57.
Fine adjustment is possible by adjusting the opening.

When the manual valve 56 is shifted to the ascending control position B, the discharge port 51 and the supply port 65
Since the space is communicated via the first large groove 91 ₁ , the transmission speed of hydraulic pressure is increased, and the rising speed of the rear lifting arm 21r is accelerated. However, even in this case, since the throttle valve 57 moderately throttles the throttle hole 70 and regulates the upper limit of the transmission speed of the hydraulic pressure, a sudden rise of the rear elevation arm 21r is suppressed.

During the above operation, the discharge pressure of the hydraulic pump 33 is transmitted through the through hole 95 to the conical valve 98 of the first relief valve 59.
Since it acts on the front surface, if the discharge pressure rises above the specified value determined by the set load of the valve spring 99, the conical valve 98 will resist the force of the valve spring 99.
The valve is opened and the excess discharge pressure is discharged to the front oil chamber 72 side through the valve chamber 93 and the through hole 96. When the discharge pressure of the hydraulic pump 33 returns to the specified value due to this pressure release, the conical valve 98 returns to the closed state by the force of the valve spring 99.

During such opening/closing operations of the conical valve 98, the small piston 98b integrated therewith slides in the guide hole 94, thereby preventing the conical valve 98 from tilting. In addition, the oil flowing through the sliding gap between the small piston 98b and the guide hole 94 can also prevent the conical valve 98 from being disturbed.

Next, in order to lower the rear lifting arm 21r, the second
When the control lever 32 is rotated clockwise in FIG. 5, the tensile force of the tension spring 129 becomes the second
Since it is applied to the control lever 32, the lever 3
2 and the spool valve 56 are easily operated. Between the neutral position A and the downward control position C of the spool valve 56, the annular portion 129a of the tension spring 129
slides on the locking shaft 130 and the tension spring 129
is in a compressed state and therefore the second control lever 3
No tensile force is applied to 2.

Then, when the manual valve 56 is shifted beyond the neutral position A to the descending control position C, the supply port 65 and therefore the check valve 58 are first cut off from the discharge port 51 by the second land ₉₀₂ . At the same time, it is communicated with the front oil chamber 72 via the second small groove 92 ₂ , and then the protruding shaft 114 of the sub valve 107 in the check valve 58 is opened by the valve opening rod 115 .
is pushed to forcibly open the sub-valve 107. In this case, since the tension force of the tension spring 127 is applied to the check valve 56, the manual valve 5
6 can be easily performed, and the pressure receiving area facing into the valve cylinder 105 of the sub-valve 107 is relatively small.
Therefore, the secondary valve 10 due to the high oil pressure inside the valve cylinder 105
Since the valve closing force 7 is relatively small, the auxiliary valve 107 can be easily opened by a light pushing force of the valve opening rod 115.

When the sub-valve 107 opens, the rear hydraulic cylinder 22r
The hydraulic pressure of the switching valve 55, the throttle hole 70, and the high pressure port 6
7. It passes through the through hole 110 of the valve cylinder 105, the through hole 113 of the main valve 106, the auxiliary valve seat 112, the supply port 65, and the second small groove ₉₂₂ in order and is released into the front oil chamber 72, so that the rear part can be raised and lowered. The arm 21r can be lowered, and its lowering speed is controlled slowly by the throttle action of the auxiliary valve 107 and the second small groove ₉₂₂ .

The opening degree of the auxiliary valve 107 is controlled to be small by the large diameter portion 114a of the protruding shaft 114 at the early stage of opening, and is controlled to be large by the small diameter portion 114b at the later stage of opening. Accordingly, the throttling action by the auxiliary valve 107 changes to two levels of strength and weakness, thereby making it possible to slowly control the descending speed of the rear lifting arm 21r to two levels of slow speed. Furthermore, the speed can be minutely adjusted by adjusting the opening of the throttle hole 70 using the throttle valve 57.

When the sub-valve 107 opens, the pressure difference between the inside and outside of the main valve 106 decreases, so if the valve-opening rod 115 is further advanced and the main valve 106 is pushed, it can be opened easily.

When the main valve 106 opens, the rear hydraulic cylinder 2
Since the hydraulic pressure 2r is quickly released through the main valve seat 109, the lowering speed of the rear lifting arm 21r is increased. However, at that time, the second small groove 9
2 ₂ is still interposed between the supply port 65 and the front oil chamber 72, the increase in the descending speed of the rear lifting arm 21r can be appropriately suppressed by its throttling action.

When the manual valve 56 is shifted to the lowering control position C, the supply port 65 and the front oil chamber 72 are interlocked via the second large groove ₉₁₂ , so that the hydraulic pressure is not released from the rear hydraulic cylinder 22r. The speed is further increased, and the lowering speed of the rear lifting arm 21r becomes maximum. This maximum downward speed is limited by the opening degree of the throttle hole 70 adjusted by the throttle valve 57.

As mentioned above, the raising and lowering of the rear lifting arm 21r has been described, but by switching the switching valve 55, the central port 6
8 to the front output port 71f, it will be understood that the front lifting arm 21f can be raised and lowered by the same action as described above. in this case,
Since the locking shaft 130 of the switching valve 55 is disposed coaxially with the switching valve 55, the tension spring 129 has no effect on the operation of the first control lever 31.

When the front and rear lifting arms 21f, 21r are stopped at appropriate raised positions and the tractor 1 is left for a long time, the throttle valve 57 is sufficiently tightened to close the throttle hole 70. If you do this, for example, the 9th
As shown in the figure, even though the rear output port 71r connected to the rear hydraulic cylinder 22r communicates with the central port 68 via the switching valve 55, if the rear output port 71r is connected to the rear hydraulic cylinder 22r, it may intervene between the second relief valve 60 and the switching valve 55 on the hydraulic circuit. Since the throttle valve 57 reliably prevents hydraulic pressure from being released from the rear hydraulic cylinder 22r, the rear lifting arm 21f
can be held immobile for a long time regardless of the magnitude of the load applied to it. On the other hand, since the front output port 71f connected to the front hydraulic cylinder 22f is closed by the switching valve 55, the front lifting arm 21f can also be held immobile for a long time regardless of the magnitude of the load applied thereto.

In the hydraulic system of such an agricultural tractor 1,
The hydraulic pump 33 and the manual valve 56, check valve 58, second relief valve 60, throttle valve 57 and switching valve 55 constituting the control valve device 34 are accommodated in a common casing 35.
3 and the control valve device 34 can be integrated into a single unit to obtain a compact hydraulic control unit 25.

In addition, since the discharge port 51 is bored in the common casing 35 as an oil passage communicating between the hydraulic pump 33 and the control valve device 34, high oil pressure can be reliably supplied from the hydraulic pump 33 to the control valve device 34 without using a hydraulic conduit. can be supplied.

C. Effects of the invention According to the invention, when shifting the manual valve from the neutral position to the descending control position, a biasing force is applied to the manual valve in the shift direction, so that the manual valve can be operated easily. It can be carried out.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, in which Fig. 1 is a side view of an agricultural tractor, Fig. 2 is a plan view of a unitized hydraulic pump and control valve device in the hydraulic system of the agricultural tractor, and Fig. 3 is a plan view of a unitized hydraulic pump and control valve device in the hydraulic system of the agricultural tractor. The figure and FIG. 4 are cross-sectional views taken along lines - and - of FIG.
Fig. 5 is a view taken along the arrow in Fig. 2, Fig. 6 is a sectional view taken along the - line in Fig. 4, Fig. 7 is a sectional view taken along the - line in Fig. 3, and Fig. 8 is a sectional view taken along the - line in Fig. 7. , FIG. 9 is a vertical sectional view of the control valve device, FIG. 9A is an enlarged view of a part of FIG. 9, FIGS. 10 and 11 are sectional views taken along lines - and - in FIG. 9, and FIG. is a hydraulic circuit diagram of the hydraulic system. A... Neutral position, B... Lift control position, C...
Lowering control position, L...Control oil path, 22f, 22r
...Front and rear hydraulic cylinders, 26...Oil tank,
33...Hydraulic pump, 51...Discharge port, 56
...Manual valve, 58...Check valve, 115
...Valve opening rod, 127...Tension spring as biasing means.

Claims (1)

[Scope of utility model registration request] a hydraulic pump; a hydraulic cylinder to which hydraulic pressure is transmitted to raise the working machine and to which hydraulic pressure is released to lower the working machine; interposed in a control oil path between the discharge port of the hydraulic pump and the hydraulic cylinder; a check valve that prevents release of hydraulic pressure from the hydraulic cylinder; a manual valve interposed in the control oil passage between the check valve and the discharge port; and a manual valve that operates in conjunction with the manual valve to force the check valve. a valve opening rod that opens automatically; the manual valve has a neutral position in which the check valve is communicated with the oil tank; and a lift control in which the manual valve is shifted to one side from the neutral position and communicates the check valve with the discharge port. and a lower control position in which the check valve is communicated with the oil tank by being shifted from the neutral position to the other position and the check valve is opened by the valve opening rod. A hydraulic system for a work vehicle, characterized in that the manual valve is provided with a biasing means for biasing the manual valve from the neutral position to the descending control position.